Hearthstone’s latest expansion, The Boomsday Project, has officially been released this week. The expansion adds 135 new cards. Log in to Hearthstone for a limited time to receive three Boomsday Project card packs for free, as well as a free random Legendary card.

“Today, Hearthstone players everywhere can unleash their inner evil genius in The Boomsday Project,” said Mike Morhaime, CEO and co-founder of Blizzard Entertainment. “We packed this expansion with all kinds of things that go boom, and we can’t wait to see the new strategies that players concoct.”

The Boomsday Project expansion adds several new care features and mechanics. Omega cards become stronger when played at a full 10 mana crystals. New Mech minions include the Magnetic keyword, letting them be combined to form more powerful minions. Projects are spells that help both players. New Legendary cards include both mad scientists and powerful new Legendary Spells.

The new single player scenario is called The Puzzle Lab, and it’s coming in another two weeks. Blizzard is still only teasing the details. Players will “will face a series of increasingly difficult puzzles as they attempt to impress Dr. Boom with their quick wits and neglect of safety regulations.”

The Boomsday Project is available now on PC and mobile devices. Like every Hearthstone expansion, cards can be purchased in individual packs or in bundles through the Shop or using real currency. Boomsday Project cards can be earned in the Arena or crafted using Arcane Dust.